1. Field of the Invention
The present invention relates to a trim-tilt device for a marine propulsion unit such as an outboard motor or outboard or inboard engine.
2. Description of the Related Art
Conventionally, the trim-tilt device for a marine propulsion unit has a cylinder device interposed between a hull and the propulsion unit which is tiltably supported by the hull. By executing supply and discharge control of a hydraulic fluid from a hydraulic fluid supply/discharge device to a cylinder device or vice versa, the cylinder device is expanded and contracted to thereby trim and tilt the marine propulsion unit. The trimming operation serves to cause the marine propulsion unit during sailing to be tilted against the propulsion force within a prescribed trim region and thereby trimmed upward and downward so as to adjust the sailing posture of the marine propulsion unit with respect to a change in the load in the water surface and thereby obtain the most favorable state of sailing. A relatively large magnitude of driving force is needed for the cylinder device. Also, the tilting operation causes the marine propulsion unit that is in the process of anchoring, to be tilted against gravitational force within a prescribed tilt region and thereby tilted upward and downward so as to raise the marine propulsion unit from the water surface. A relatively small magnitude of driving force is sufficient for the cylinder device.
Further, in a trim-tilt device whose cylinder device having a single-cylinder in order to enhance the outer appearance and to make the trim-tilt device compact in size, there is a type which is described in U.S. Pat. No. 325,240.
The conventional cylinder device comprises a housing connected to one of the hull and the marine propulsion unit and forms a large-diameter trim chamber; a cylinder that is telescopically inserted into the trim chamber of the housing and forms a small-diameter tilt chamber, a large-diameter trim piston that is fixed to an end portion of the cylinder within the trim chamber of the housing and that partitions the trim chamber into a first trim chamber of a cylinder accommodation side and a second trim chamber of an anti cylinder accommodation side; a piston rod that is connected to the other of the hull and the marine propulsion unit and that is telescopically inserted into the tilt chamber of the cylinder; and a small-diameter tilt piston that is fixed to an end of the piston rod within the tilt chamber of the cylinder and that partitions the tilt chamber into a first tilt chamber of a piston rod accommodation side and a second tilt chamber of an anti piston rod accommodation side. A standing pipe fixed to the trim piston is slidably passed through the tilt piston. By the intrapipe passage of the standing pipe, the first trim chamber and the first tilt chamber are communicated with each other, whereby the first trim chamber and the first tilt chamber are communicated with a supply side of the hydraulic fluid supply/discharge device during a contraction stroke of the trimming operation and tilting operation, and are communicated with a discharge side thereof during an expansion stroke of each thereof. The second trim chamber and the second tilt chamber are communicated with each other by way of the communication passage formed in the trim piston by being passed there through, whereby it has been arranged that the second trim chamber and the second tilt chamber are communicated with the supply side of the hydraulic fluid supply/discharge device during the expansion stroke of each trimming operation and tilting operation and are communicated with the discharge side thereof during the contraction stroke of each thereof.
In this prior art, since the first trim chamber and the first tilt chamber communicate with each other by the standing pipe fixed to the trim piston, there is suppression of exposure to the outside of the cylinder device of the hydraulic fluid that is supplied and discharged between the hydraulic fluid supply/discharge device and the cylinder device.
However, the conventional technique has the following problems.
(1) In order to reduce the number of pipes exposed around the cylinder device, the standing pipe fixed to the trim piston is slidably passed through the tilt piston, with the result that the construction of the cylinder device is complex.
(2) The portions of the cylinder device that are needed to be fluid-tightly sealed become five in total number as a result of adding a portion where the standing pipe slides with respect to the through-hole of the tilt piston to four portions: where the cylinder slides with respect to the cylinder guide provided in the housing; where the trim piston slides with respect to the inner surface of the trim chamber of the housing, where the piston rod slides with respect to the rod guide provided in the cylinder and where the tilt piston slides with respect to the inner surface of the tilt chamber of the cylinder. Because of this, sealing becomes a serious problem.
(3) During the tilting operation, the tilt piston is moved up and down in such a way that its outer-peripheral portion is in sliding contacted with the inner surface of the tilt chamber of the cylinder and its inner-peripheral portion is in sliding contacted with the standing pipe. Therefore, if the concentricity between the cylinder and the standing pipe is bad, the assemblability and slidability thereof are also bad, resulting in the impairment of the tilt-operating efficiency.